Engine cylinder head structure

ABSTRACT

In a cylinder head structure of an engine, a structure of an oil passage is simplified to downside the engine and to provide proper flow of cooling water in the cylinder head. A partition wall is disposed in the cylinder head to separate an upward valve operating chamber from a downward water jacket. A boss section is formed at a position lower than the partition wall in an edge wall of the cylinder head, and has one end joined to a chain case and the other end protruding into the water jacket. A branch oil passage is formed in the boss section. The branch oil passage has a valve upstream-side passage section specified by a section toward the chain case with respect to a junction with a cylinder head-side oil passage. The linear communication passage section communicates between an end portion of the branch oil passage protruding into the water jacket and a camshaft cap coupling surface of a second camshaft bearing section.

FIELD OF THE INVENTION

This invention relates to a structure of a cylinder head of an engine,and more particularly to a structure of the cylinder head of an enginewith a variable valve timing mechanism.

BACKGROUND OF THE INVENTION

An engine with a hydraulically-driven variable valve timing mechanismincludes an actuator disposed at an end of a camshaft, an actuator oilpassage as an operating oil path for introducing oil from an oil pump tothe actuator, and a camshaft oil passage as a lubricating oil path forintroducing the oil to the camshaft.

Conventionally, an engine comprises structures forming an oil passagefor the engine, which include an operating oil path in communication toan end journal at an end of a camshaft in a cylinder head to introducethe oil to an actuator for a variable valve timing mechanism, and acamshaft lubricating oil path in communication to a camshaft housing ofa journal adjacent to the end journal.

Also there are some structures of an oil passage for the engine, whichinclude an operating oil path in communication to a camshaft housingjournal section of the end journal of the camshaft to introduce the oilto the actuator for the variable valve timing mechanism, and alubricating oil path also in communication to the end journal of thecamshaft.

Prior Art

The following documents 1 and 2 form the prior art of which the presentapplicant has presently knowledge

Document 1: JP No. 2000-110536A

Document 2: JP No. 2000-199417A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Conventionally, in the structure of the oil passage as disclosed in JPNo. 2000-110536A, an oil pipe is disposed in the lubricating oil path ofthe camshaft. It therefore increases the number of components and alsorequires arrangement of oil pipes so as not to interfere with thecamshaft and a cylinder head cover, resulting in constraint of layout.

Also according to JP No. 2000-199417A, the end journal of the camshaftis increased in length to disadvantageously lengthen the engine. Wherethe end journal is made shorter in length, the operating oil pressurefor the variable valve timing mechanism cannot be fully obtained.

To obviate above-mentioned inconveniences in a cylinder head of anengine equipped with a variable valve timing mechanism, the presentinvention provides a simplified structure of an oil passage including anactuator oil passage for introducing the oil to an actuator for thevariable valve timing mechanism and a camshaft bearing oil passage forlubricating a camshaft bearing section of a camshaft, while fullyobtaining the operating oil pressure for the variable valve timingmechanism. This reduces the number of components and allows the cylinderhead to be made smaller in size to downsize the engine, which promotesproductivity. A boss section having the oil passage therein providesproper flow of cooling water in the cylinder head.

Means to Solve the Problems

The present invention provides a structure of a cylinder head of anengine, having more than one camshaft bearing section formed on top ofthe cylinder head and arranged in an axial direction of a camshaft, thecamshaft bearing section rotatably supporting the camshaft; an actuatorof a variable valve timing mechanism attached to the camshaft at aprotruding section from an edge wall of the cylinder head; an oilcontrol valve disposed in a chain case that covers the edge wall of thecylinder head; a cylinder head-side oil passage formed in the edge wallof the cylinder head by which oil is supplied from the cylinder blockside, the cylinder head-side oil passage having a downstream endbranched into an actuator oil passage in communication to the actuatorthrough the oil control valve and a camshaft bearing oil passage incommunication to the camshaft bearing section; a valve upstream-sidepassage section formed in the edge wall of the cylinder head as theactuator oil passage for communicating between the cylinder head-sideoil passage and the oil control valve; a valve downstream-side passagesection for communicating between the oil control valve and a firstcamshaft bearing section above the edge wall of the cylinder head; acommunication passage section as the camshaft bearing oil passage forcommunicating the cylinder head-side oil passage with a second camshaftbearing section adjacent to the first camshaft bearing section in theaxial direction of the camshaft, comprising the improvement wherein apartition wall is disposed in the cylinder head to separate an upwardvalve operating chamber from a downward water jacket; a boss section isformed at a position lower than the partition wall in the edge wall ofthe cylinder head, and has one end joined to the chain case and theother end protruding into the water jacket; a branch oil passage isformed in the boss section and extends linearly into the water jacketfrom a joint surface with the chain case, and has a middle section towhich the cylinder head-side oil passage is connected, the branch oilpassage having the valve upstream-side passage section specified by asection toward the chain case with respect to a junction Keith thecylinder head-side oil passage; and the linear communication passagesection communicates between an end portion of the branch oil passageprotruding into the water jacket and a camshaft cap coupling surface ofthe second camshaft bearing section.

EFFECTS OF THE INVENTION

According to the structure of the cylinder head of the engine of thepresent invention, the oil passage structure including the actuator oilpassage and the camshaft bearing oil passage can be simplified whilefully maintaining the operating oil pressure to the variable valvetiming mechanism, reducing the number of components and providing asmaller cylinder head to downsize the engine promoting productivity. Theboss section having the oil passage therein provides proper flow ofcooling water in the cylinder head.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to downside the engine and to promote productivity, the presentinvention provides the simplified structure of the oil passage includingthe actuator oil passage for conducting the oil to the actuator of thevariable valve timing mechanism and the camshaft bearing oil passage forlubricating the camshaft bearing section. In order to provide properflow of the cooling water in the cylinder head, the present inventionprovides the boss section having the oil passage therein.

Embodiments of the present inventions are explained in detail withreference to drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a cylinder head taken along line 1-1of FIG. 2.

FIG. 2 is a right side view of a cylinder head according to a firstembodiment of the present invention.

FIG. 3 is a perspective view of a cylinder head according to a firstembodiment of the present invention.

FIG. 4 is a plan view of a cylinder head according to a first embodimentof the present invention.

FIG. 5 is a cross-sectional view of a cylinder head according to a firstembodiment of the present invention.

FIG. 6 is a right side view of an engine from which a chain case isdetached according to a first embodiment of the present invention.

FIG. 7 is a right side view of an engine according to a first embodimentof the present invention.

FIG. 8 is a perspective view of a cylinder head according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF A FIRST EMBODIMENT OF THE INVENTION

FIGS. 1-5 illustrate a first embodiment of the present invention. FIGS.6 and 7 show a multi-cylinder engine 1 for mounting on a vehicle.

The engine 1 is installed transversely of the vehicle and includes acylinder block 2, a cylinder head 3, a cylinder head cover 4, and an oilpan 5. To the engine 1, a chain case 7 is attached which defines a chainchamber 6 over a right side of the cylinder block 2 and the cylinderhead 3. As shown in FIG. 1, the chain case 7 is joined to a joiningsurface 8A of an edge wall 8 of the cylinder head 3.

Referring to FIG. 1, the cylinder head 3 has combustion chambers 9,corresponding to respective cylinders, formed in a lower sectionthereof. The cylinder head 3 also has in an upper section an ignitionplug hole wall 11 defining an ignition plug hole 10, and a valveoperating chamber 12 on the periphery of the ignition plug hole wall 11.

As shows in FIG. 5, the cylinder head 3 includes an intake port 13 forrespective cylinders formed on an intake side, a rear side, forconducing the intake air to the combustion chambers 9, and an exhaustport 14 for respective cylinders formed on an exhaust side, a frontside, for conducting the exhaust gas from the combustion chambers 9.

Further referring to FIG. 1, the cylinder head 3 includes a water jacket15 around the intake port 13, and a cooling water introducing passage 16for conducting the cooling water to the water jacket 15. The coolingwater introducing passage 16 comprises an intake-side cooling waterintroducing passage 16A and an exhaust-side cooling water introducingpassage 16B.

As shown in FIG. 7, the chain case 7 includes, in an upper part towardthe cylinder head 3, a protuberance section 17 formed rearwardly on theintake side, and a depressed section 18 and an engine mount attachingsection 19 which are formed forwardly on the exhaust side.

As shown in FIGS. 6 and 7, in an upper side of the cylinder block 2 andin the rearward intake side, a water pump 22 equipped with a water pumppulley 21 is mounted through a water pump mounting section 20. The waterpump mounting section 20 includes a pump mounting surface 23, a pumpinlet 24, and pump outlet 25. The water pump 22 supplies the coolingwater to the cooling water introducing passage 16 in the cylinder head3.

In the cylinder block 2, an alternator 29 with an alternator pulley 28is attached rearwardly of the water pump 22, which is supported by anupper alternator arm 26 and a lower alternator arm 27.

As shown in FIGS. 6 and 7, a crankshaft 30 is supported in the cylinderblock 2. The crankshaft 30 includes on a right side a crank pulley 31, atrochoid oil pump 32, and a timing sprocket 33. The oil pump 32 isformed by an oil pump plate 34 in a lower part of the chain case 7 andis driven by rotation of the crankshaft 30 to generate the oil pressure.

Also as shown in FIG. 6, the cylinder block 2 includes a main gallery 35formed in an axial direction X of a camshaft (transversely of thevehicle) for introducing the oil from the oil pump 32. The cylinderblock 2 also includes a cylinder block-side oil passage 36 extendingupwardly and branched from the main gallery 35.

Further as shown in FIG. 6, at the bottom of the cylinder block 2, anintake pipe 38 equipped with an oil strainer 37 is attached so as to beconnected to the oil pump 32.

As shown in FIG. 7, a belt 39 passes around the water pump pulley 21,the alternator pulley 28, and the crank pulley 31.

Referring to FIG. 4, in the upper part of the cylinder head 3, aplurality of camshaft bearing sections 40, i.e. a first camshaft bearingsection 40A, a second camshaft bearing section 40B, etc., are arrangedin the axial direction X of the camshaft (transverse direction of thevehicle).

Lower portions of the camshafts, an intake camshaft 41 and an exhaustcamshaft 42 are rotatably supported by the first camshaft bearingsection 40A, the second camshaft bearing section 40B, etc.

As shown in FIG. 1, upper portions of the intake camshaft 41 and theexhaust camshaft 42 are rotatably supported by a plurality of camshafthousings 43, i.e. a first camshaft housing 43A, a second camshafthousing 43B, etc.

As shown in FIG. 6, the intake camshaft 41 has a right end to which anintake camshaft sprocket 44 is attached; the exhaust camshaft 42 has aright end to which an exhaust camshaft sprocket 45 is attached.

In the chain chamber 6, a timing chain 46 passes around the timingsprocket 33, the intake camshaft sprocket 44, and the exhaust camshaftsprocket 45.

Referring to FIGS. 3 and 4, an actuator 48 of a variable valve timingmechanism 47 is attached to the intake camshaft 41 at a portionprotruding from the edge wall 8 of the cylinder head 3.

As shown in FIGS. 2, 6, and 7, an oil control valve 49 of the variablevalve timing mechanism 47 is attached to the chain case 7 that coversthe edge wall 8 of the cylinder head 3. The oil control valve 49integrates a solenoid section 50 and a spool portion 51; the spoolportion 51 is inserted inner of the chain case 7 from a stepped portionof the depressed section 18 outside the chain case 7, while the solenoidsection 50 is positioned in the depressed section 18.

As shown in FIGS. 1 and 6, in the edge wall 8 of the cylinder head 3, acylinder head-side oil passage 52 is formed by which the oil is suppliedfrom the cylinder block 2 side.

A downstream end of the cylinder head-side oil passage 52 is branchedinto an actuator oil passage (operating oil path) 53 in communication tothe actuator 48 through the oil control valve 49 and a camshaft bearingoil passage (lubrication oil path) 54 in communication to the secondcamshaft bearing section 40B.

An upstream end of the cylinder-head side oil passage 52 is communicatedto the cylinder-block side oil passage 36 of the cylinder block 2.

As shown in FIG. 1, in the edge wall 8 of the cylinder head 3, theactuator oil passage 53 includes a valve upstream-side passage section55A communicating between the cylinder head-side oil passage 52 and theoil control valve 49, and a valve downstream-side passage section 55Bcommunicating between the oil control valve 49 and the first camshaftbearing section 40A that is positioned above the edge wall 8 of thecylinder head 3.

As shown in FIGS. 2, 3, and 6, the valve downstream-side passage section55B includes a valve timing retard passage 56 and a valve timing advancepassage 57, which extend upwardly for introducing the oil from the oilcontrol valve 49 to the actuator 48 side.

Also as shown in FIG. 2, a camshaft housing retard passage 58 incommunication to the valve timing retard passage 56, and a camshafthousing advance passage 59 in communication to the valve timing advancepassage 57 are formed in the first camshaft housing 43A.

Further, as shown in FIG. 4, an end journal 41A, or a first camshaftjournal at a right end of the intake camshaft 41 includes an end journalretard passage 60 in communication to the camshaft housing retardpassage 58, and an end journal advance passage 61 in communication tothe camshaft housing advance passage 59. In the end journal 41A, onlythe actuator oil passage 53 is therefore formed. Thereby, the structurecan be simplified.

The end journal retard passage 60 is communicated to a retard chamber ofthe actuator 48; the end journal advance passage 61 is communicated toan advance chamber of the actuator 48.

Referring to FIG. 1, the cylinder head-side oil passage 52 and thesecond camshaft bearing section 40B adjacent to the first camshaftbearing section 40A in the axial direction of the intake camshaft 41 arecommunicated by a communication oil passage 66 of a communicationpassage section 65 as the camshaft bearing oil passage 54.

The communication oil passage 66 is communicated to a second camshafthousing lubricating passage 64B formed in the second camshaft housing43B supporting the second camshaft journal 41B of the intake camshaft41. In addition, the communication oil passage 66 is formed inward ofthe water jacket 15.

As shown in FIG. 1, the cylinder head 3 includes a partition wall 67which separates the upward valve operating chamber 12 from the downwardwater jacket 15.

Also, in the edge wall 8 of the cylinder head 3 in a section lower thanthe partition wall 67, a boss section 68 of a certain area is formedwhich has one end joined to the chain case 7 and the other endprotruding into the water jacket 15. The boss section 68 is formed toprotrude into the water jacket 15 so as to permit proper flow of thecooling water in the water jacket 15.

Within the boss section 68, a branch oil passage 69 is formed whichlinearly extends into the water jacket 15 from the joining surface 8Awith the chain case 7 and which has an intermediate portion to which thecylinder head-side oil passage 52 is connected. The branch oil passage69 extends to the vicinity of the combustion chamber 9 of the waterjacket 15, that is adjacent to the ignition plug hole 10.

The branch oil passage 69 toward the chain case 7 with respect to ajunction with the cylinder head-side oil passage 52 forms the valveupstream-side passage section 55A.

Also, an end section of the branch oil passage 69 protruding into thewater jacket 15 and a camshaft cap coupling surface 70 of the secondcamshaft bearing section 40B are communicated by the linearcommunication passage section 65.

Referring to FIG. 4, when viewing the cylinder head 3 from a side of amounting surface 4A of the cylinder head cover 4, a centerline 68C ofthe boss section 68 is offset with respect to a center 11C of theignition plug hole wall 11 by a distance L in a direction perpendicularto the axial direction X of the camshaft (in the longitudinal directionof the vehicle) toward the axis of the intake camshaft 41 to which theactuator 48 is attached.

Referring to FIG. 1, the branch oil passage 69 is formed in a steppedshape by a first branch oil passage 71 and a second branch oil passage72; a diameter D2 of the second branch oil passage 72 at the junctionwith the communication oil passage 66 is reduced with respect to adiameter D1 of the first branch oil passage 71 at the junction with thecylinder head-side oil passage 52.

The first branch oil passage 71 is communicated to the oil control valve49 through a case oil passage of the chain case 7.

In this connection, as shown in FIGS. 1 and 4, a camshaft bearinglubrication passage 63 that extends upwardly is connected to the secondbranch oil passage 72 at a center portion in the axial directionthereof; the camshaft bearing lubrication passage 63 is communicated toan exhaust camshaft bearing section 73A that supports the exhaustcamshaft 42 thorough a first camshaft housing lubricating passage 73that is formed in the first camshaft housing 43A.

As shown in FIG. 6, the timing chain 46 is maintained under a certaintension by a forward chain guide 74 and a rearward tensioner mechanism77 including a chain tensioner 75 and a tensioner arm 76.

Operation of the first embodiment of the present invention is explainedas follows.

The oil in the oil pan 5 is sucked by the driven oil pump 32 through theoil strainer 37, and is pumped to the main gallery 35 in the cylinderblock 2.

The oil in the main gallery 35 is introduced through the cylinderblock-side oil passage 36 to the cylinder head-side oil passage 52 inthe cylinder head 3.

The oil having been introduced to the cylinder head-side oil passage 52is branched by the branch oil passage 69 into the actuator oil passage53 for conducing the oil toward the chain case 7 and the camshaftbearing oil passage 54 for conducting the oil toward the first andsecond camshaft bearing sections 40A, 40B of the cylinder head 3.

The oil having been introduced to the actuator oil passage 53 is dividedby the oil control valve 49 into the valve timing retard passage 56 andthe valve timing advance passage 57.

The oil is then introduced to the retard chamber and the advance chamberof the actuator 48 for the variable valve timing mechanism 47 throughthe end journal advance passage 60 and the end journal advance passage61 of the end journal 41A of the intake camshaft 41 so as to change thetiming of valve operations.

On the other hand, the oil having been introduced to the camshaftbearing oil passage 54 is introduced to the second camshaft journal 41Bof the intake camshaft 41 through the communication oil passage 66 andthe second camshaft housing lubricating oil passage 64B in the secondcamshaft housing 43B.

Further, some of the oil having been introduced to the camshaft bearingoil passage 54 is introduced to the camshaft bearing section 73A towardthe exhaust camshaft 42 through the camshaft bearing lubrication passage63 and the first camshaft housing lubricating oil passage 73 in thefirst camshaft housing 43A.

Thereby, the lubricating oil path for the intake camshaft 41 to whichthe actuator 48 of the variable valve timing mechanism 47 is attached isguided to the second camshaft journal 41B of the intake camshaft 41 bythe branch oil passage 69 that extends inside the water jacket 15 of thecylinder head 3 and by the communication oil passage 66, whichsimplifies the structure of the oil passage.

Also the branch oil passage 69 extends to the vicinity of the combustionchamber 9 of the water jacket 15, i.e. adjacent to the ignition plughole 10, which brings the flow of the cooling water to the vicinity ofthe combustion chamber 9, in particular the ignition plug hole wall 11,when the cooling water introduced by the water pump 22 on the intakeside flows toward the exhaust side.

More particularly, according to the first embodiment of the presentinvention, in the cylinder head 3 equipped with the variable valvetiming mechanism 47, the end journal 41A of the intake camshaft 41 isprovided with only the actuator oil passage 53 for the actuator 48 ofthe variable valve timing mechanism 47; the camshaft bearing oil passage54 has the communication oil passage 66 formed inward of the waterjacket 15 in the cylinder head 3 for conducting the oil to the secondcamshaft journal 41B. Thereby, the camshaft bearing oil passage 54 issimplified while fully obtaining the operating oil pressure for thevariable valve timing mechanism 47, reducing the number of componentsand allowing the cylinder head 3 to be made smaller in size to downsizethe engine 1 and promote productivity. Also the boss section 68 havingthe branch oil passage 69 therein provides proper flow of the coolingwater in the cylinder head 3 to improve coolability of the combustionchamber 9 in the cylinder head 3.

While the first embodiment of the present invention has been explainedabove, the constitution of this embodiment is applied to each claim asfollows.

Firstly, the present invention provides the partition wall 67 whichseparates the upward valve operating chamber 12 from the downward waterjacket 15; in the edge wall 8 of the cylinder head 3 in the sectionlower than the partition wall 67, the boss section 68 of the certainarea is formed to protrude into the water jacket 15, which has one endjoined to the chain case 7 and the other end protruding into the waterjacket 15; within the boss section 68, the branch oil passage 69 isformed which linearly extends into the water jacket 15 from the joiningsurface 8A with the chain case 7 and which has the intermediate portionto which the cylinder head-side oil passage 52 is connected; and thevalve upstream-side passage section 55A is specified by the section ofthe branch oil passage 69 toward the chain case 7 with respect to thejunction of the branch oil passage 69 and the cylinder head-side oilpassage 52. Also, the end section of the branch oil passage 69protruding into the water jacket 15 and the camshaft cap couplingsurface 70 of the second camshaft bearing section 40B are communicatedby the linear communication passage section 65.

By such constitution, the valve upstream-side passage section 55A thatis upstream of the actuator oil passage 53 and the upstream section ofthe camshaft bearing oil passage 54 are integrated into the branch oilpassage 69 extending linearly into the boss section 68, which simplifiesthe oil passage structure of the cylinder head 3.

In addition, the branch oil passage 69 is positioned at the lower levelthan the partition wall 67 that separates the valve operating chamber 12in the cylinder head 3 from the water jacket 15, and the branch oilpassage 69 protrudes into the water jacket 15, so that the camshaft capcoupling surface 70 of the second camshaft bearing section 40B and theinner edge section of the branch oil passage 69 can be communicated bythe linear communication passage section 65, which simplifies thestructure of the camshaft bearing oil passage 54.

Further, this may decrease the possibility of fall or deterioration ofworking tools from a perpendicular direction to the camshaft capcoupling surface 70 when shaping the communication oil passage 66, whichpromotes workability.

Also the branch oil passage 69 and the communication oil passage 66protrude into the water jacket 15, which simplifies the oil passagestructure formed in the upper part of the edge wall 8 of the cylinderhead 3 and allows the cylinder head 3 to be made smaller in size topromote the productivity.

Moreover, the boss section 68 causes the cooling water, which isintroduced from the cooling water introducing passage 16 of the cylinderhead 3 adjacent to the water pump 22 and flows in the directionperpendicular to the rows of the cylinders (in the longitudinaldirection of the vehicle), to be deviated toward the center of thecombustion chamber 9, which enhances the cooling effect at the center ofthe combustion chamber 9.

According to the invention defined in claim 2, when viewing the cylinderhead 3 from the side of the mounting surface 4A of the cylinder headcover 4, the centerline 68C of the boss section 68 is offset withrespect to the center of the ignition plug hole wall 11 in the directionperpendicular to the axial direction X of the camshaft (in thelongitudinal direction of the vehicle) toward the axis of the intakecamshaft 41 to which the actuator 48 is attached.

Thereby, the communication passage section 65 can be positioned adjacentto the ignition plug hole wall 11 in the axial direction X of thecamshaft, which reduces the longitudinal dimension of the cylinder head3 and reduces the entire length of the communication oil passage 66,promoting the workability and improving the productivity of the cylinderhead 3.

According to the invention defined in claim 3, the branch oil passage 69is formed in the stepped shape; the diameter of the branch oil passage69 at the junction with the communication oil passage 66 is reduced withrespect to the diameter of the passage at the junction with the cylinderhead-side oil passage 52.

This is intended to enhance responsivity of the actuator 48 of thevariable valve timing mechanism 47 by reducing the diameter of thebranch oil passage 69 on a joint side of the communication oil passage66 so as to supply more oil through the actuator oil passage 53. Also,thanks to the structure of the present invention, the actuator oilpassage 53 can be made greater in diameter than the camshaft bearing oilpassage 54 merely by processing the branch oil passage 69 by using thecutting tools in a stepped shape, which promotes the productivity of thecylinder head 3.

DETAILED DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION

FIG. 8 illustrates a second embodiment of the present invention.

In the second embodiment, the elements identical or similar to the firstembodiment are designated by the same reference numbers.

The second embodiment of the present invention is characterized asfollows. In the edge wall 8 of the cylinder head 3, a branch oil passage81 is formed which is communicated to the cylinder head-side oil passage52 and which conducts the oil toward the oil control valve 49; acamshaft bearing oil groove 82 is formed which is communicated to thebranch oil passage 81; and a camshaft bearing oil passage 83 is formedwhich is communicated to the camshaft bearing oil groove 82. Thecamshaft bearing oil groove 82 is formed to have a certain area in awidth W, and functions as a throttling valve to restrict the oilrequired for lubricating the camshaft. The camshaft bearing oil groove83 is formed within the water jacket 15 of the cylinder head 3.

In the edge wall 8 of the cylinder head 3, the valve timing retardpassage 56 and the valve timing advance passage 57 are formed forconducting the oil from the oil control valve 49 toward the actuator 48.

According to the second embodiment, the oil pumped from the cylinderblock 2 is introduced to the branch oil passage 81, and is divided atthe control valve 49 into the valve timing retard passage 56 and thevalve timing advance passage 57. Also, the oil pumped from the cylinderblock 2 is introduced through the camshaft bearing oil groove 82 to thecamshaft bearing oil passage 83. At this moment, the flow rate of theoil for the camshaft bearing is restricted by the camshaft bearing oilgroove 82.

Thereby, the camshaft bearing oil groove 82 functioning as conventionalthrottling valve eliminates the need for the throttling valve, reducingthe number of components and simplifying the structure.

INDUSTRIAL APPLICABILITY

The present invention is illustrated for the cylinder head structureequipped with the variable valve timing mechanism. However, the presentinvention can be applied to the cylinder head using common materialswithout the variable valve timing mechanism, which is devoid ofprocessing of oil passage such as the valve timing retard passage, thevalve timing advance passage, and the camshaft bearing lubrication path.

EXPLANATION OF REFERENCE NUMERALS

1—engine;

2—cylinder block;

3—cylinder head;

4—cylinder head cover;

5—oil pan;

7—chain case;

9—combustion chamber;

10—ignition plug hole;

11—ignition plug hole wall;

22—water pump;

32—oil pump;

35—main gallery;

40—camshaft bearing section;

41—intake camshaft;

42—exhaust camshaft;

43—camshaft housing;

47—variable valve timing mechanism;

48—actuator;

49—oil control valve;

52—cylinder head-side oil passage;

53—actuator oil passage;

54—camshaft bearing oil passage;

55A—valve upstream-side passage section;

55B—valve downstream-side passage section;

56—valve timing retard passage,

57—valve timing advance passage;

63—camshaft bearing lubrication passage;

65—communication passage section;

66—communication oil passage;

67—partition wall;

68—boss section;

69—branch oil passage;

70—camshaft cap coupling surface; and

73—exhaust camshaft bearing lubrication passage.

1. A structure of a cylinder head of an engine, comprising: more thanone camshaft bearing section formed on top of the cylinder head andarranged in an axial direction of a camshaft, the camshaft bearingsection rotatably supporting the camshaft; an actuator of a variablevalve timing mechanism attached to the camshaft at a protruding sectionfrom an edge wall of the cylinder head; an oil control valve disposed ina chain case that covers the edge wall of the cylinder head; a cylinderhead-side oil passage formed in the edge wall of the cylinder head bywhich oil is supplied from the cylinder block side, the cylinderhead-side oil passage having a downstream end branched into an actuatoroil passage in communication to the actuator through the oil controlvalve and a camshaft bearing oil passage in communication to thecamshaft bearing section; a valve upstream-side passage section formedin the edge wall of the cylinder head as the actuator oil passage forcommunicating between the cylinder head-side oil passage and the oilcontrol valve; a valve downstream-side passage section for communicatingbetween the oil control valve and a first camshaft bearing section abovethe edge wall of the cylinder head; a communication passage section asthe camshaft bearing oil passage for communicating the cylinderhead-side oil passage with a second camshaft bearing section adjacent tothe first camshaft bearing section in the axial direction of thecamshaft, comprising the improvement wherein a partition wall isdisposed in the cylinder head to separate an upward valve operatingchamber from a downward water jacket; a boss section is formed at aposition lower than the partition wall in the edge wall of the cylinderhead, and has one end joined to the chain case and the other endprotruding into the water jacket; a branch oil passage is formed in theboss section and extends linearly into the water jacket from a jointsurface with the chain case, and has a middle section to which thecylinder head-side oil passage is connected, the branch oil passagehaving the valve upstream-side passage section specified by a sectiontoward the chain case with respect to a junction with the cylinderhead-side oil passage; and the linear communication passage sectioncommunicates between an end portion of the branch oil passage protrudinginto the water jacket and a camshaft cap coupling surface of the secondcamshaft bearing section.
 2. The structure of the cylinder bead of theengine according to claim 1, wherein when viewing the cylinder head fromthe side of a mounting surface of a cylinder head cover, a centerline ofthe boss section is offset with respect to a center of an ignition plughole wall in the direction perpendicular to an axial direction of thecamshaft toward an axis of the camshaft to which the actuator isattached.
 3. The structure of the cylinder head of the engine accordingto claim 1, wherein the branch oil passage is formed in a stepped shape,a diameter of the branch oil passage at a junction with thecommunication passage section is reduced with respect to a diameter ofthe passage at a junction with the cylinder head-side oil passage.